1. Field of the Invention
The present invention relates to a composite permanent magnet synchronous machine and, more particularly, to a composite permanent magnet synchronous machine capable of switching to a different phase, such as three-phase, six-phase, and nine-phase, thus being allowed to connect in parallel with utility power with different voltages of 110/220/440 V.
2. Description of Related Art
Electrical energy has become essential power for human beings. Currently, thermal power generation is still the most popular way for generating power in the world, and the amount of power generated is also the largest. Typically, thermal power generation is employed to burn fossil fuel, such as coal, petroleum, or natural gas; to heat up water and generate vapor for driving a power generator. However, thermal power generation may place a great burden on the environment, such as increased carbon dioxide emissions or the high probability of acid rain.
In addition to thermal power generation, nuclear power generation is also a popular way to generate power in the world. Nuclear power generation is employed to produce energy by a controllable nuclear reaction, so as to generate power, heat content, and electrical energy. However, a severe shortcoming of nuclear power generation is the need of processing nuclear waste. Nuclear waste has to be isolated from the outside environment due to the radioactivity contained therein. Although the radioactivity will decrease gradually, nuclear waste generated by nuclear power generation has to be stored for a long time, even up to thousands of years.
Due to the fast growth of power consumption by the human beings, energy consumption in the world is estimated to grow at a rate of 2% per year from 2003 to 2030. As a comparison, wind power generation systems are also developing rapidly in the world, and the development can be seen with the evidence that wind power generation grew at a rate of 24% per year on average from 4.8 GW in 1995 to 58 GW in 2005. Therefore, to increase the efficiency of wind power generation systems and to decrease the weight and volume thereof has become the major goal for future development in related fields.
A wind power generator is operated by airflow for providing available energy. When the airflow speed rises, kinetic energy increases. The kinetic energy of wind is employed to cause the rotation of a windmill, so as to drive a power generator for generating electrical energy. As compared with thermal and nuclear power generation, wind power generation causes relative low pollution to the environment and needs not to deal with waste material. Moreover, wind power is a natural energy source, and thus electricity generation by wind power will not be influenced by any shortage of fossil fuel.
In a wind power generation system, the current harmonic at the generator side is very high, which may cause undesired effects on the generator. For example, the mechanical efficiency is decreased, and the harmonic frequency is likely to cause core loss and copper loss, resulting in over heating, noise production, and mechanical vibration or similar problems on generators. Therefore, how to reduce the current harmonic at the generator side and increase the efficiency are major issues to be improved in wind power generation systems or even all other power generation systems.
Traditionally, most electric machines are of a three-phase machine structure, such as a three-phase power generator or three-phase electric motor. However, the prior three-phase machine structure is unable to satisfy the actual requirement due to the development of technology and the increased electricity consumption rate. Therefore, six-phase machine structure has been introduced. Moreover, machine structure capable of switching between three-phase and six-phase is also derived through some research, which can increase the utilization of conductors, and further increase reliability and safety when the machine structure is under operation.
However, the machine structure capable of switching between three-phase and six-phase cannot meet the requirements for industries, which desire an innovative machine structure. Accordingly, it is desired to provide an improved composite machine structure capable of switching to three-phase, six-phase, or nine-phase, wherein the machine structure with nine-phase is a novel machine structure. Since the fabrication of a single nine-phase machine structure is rather difficult due to the particular slot/pole combination and the match of electrical degree, it is surely innovative to construct a machine structure capable of switching to three-phase, six-phase, and nine-phase.
After overcoming the aforementioned problems and difficulties encountered in the prior machine structures, the present invention thus provides a composite permanent magnet synchronous machine capable of switching to three-phase, six-phase, and nine-phase, which is suitable for use not only in a wind power generator, but also in any other machine structures.